Recently, the pressure sensitive cholesteric liquid crystal (ChLC) writing tablet, Improv Electronics® Boogie Board® LCD eWriter, has appeared on the market in which a pointed stylus or the finger can be used to write or trace an image on the surface of the tablet as described in U.S. Pat. No. 6,104,448, which is incorporated herein by reference in its entirety. (Improv Electronics® is a unit of Kent Displays, Inc.) Such a stylus does not transfer any ink or other material to any surface. This tablet offers a considerable improvement over previous tablet technologies in that the image can be simply and instantly erased with the push of a button that applies a voltage pulse to electrodes in the tablet. In a ChLC tablet, the liquid crystal is commonly dispersed in a polymer network and sandwiched between two substrates that are spaced to a particular gap. The upper substrate is flexible and the bottom substrate is painted with a light absorbing (black or colored) background. The cell gap is usually set by plastic or glass spacers that are either cylindrical or spherical in shape. When one presses on the top substrate with a pointed stylus, fingernail or other object, the liquid crystal is locally displaced. Flow induced in the liquid crystal changes its optical texture from a substantially transparent to a brilliant reflective color at the location of the pressure. The reflective lighter color contrasts well to the dark background of the lower substrate. An image traced by the stylus or finger will remain on the tablet indefinitely until erased, typically consuming no power. Erasure is accomplished by applying a voltage pulse to substantially transparent conducting electrodes on the inner surface of the substrates that drive the ChLC from its color reflective state back to its substantially transparent state.
The above referenced technology and its applications are disclosed in more detail in U.S. Pat. No. 6,104,448, filed on Dec. 15, 1999, which is incorporated herein by reference in its entirety. Polymer dispersions of the cholesteric liquid crystal can be used to control the pressure sensitivity as described in U.S. Pat. No. 8,228,301, filed on May 16, 2008, and incorporated herein by reference in its entirety. Other modes of operation, including multiple color images, negative images and select erase, are described in the patent given immediately above as well as U.S. Pat. No. 8,139,039 filed on Jul. 29, 2008, and incorporated herein by reference in its entirety.
In order to provide image digitization, a touchscreen was incorporated in the back of the device as disclosed in published U.S. Patent Application Pub. No. 20120268420 A1, filed on Apr. 27, 2012 and incorporated herein by reference in its entirety. The touchscreen is locally activated when a specialized stylus applies pressure on the device surface. The pressure applied on the top substrate induces local shear driving the cholesteric liquid crystal from a dark state to a bright configuration in the stressed region. The drawing is simultaneously registered in the back touchscreen which digitizes the signal to a storage device. Therefore, an image is simultaneously observed in the writing display and captured as a digital image in a storage unit to be later recalled in a computer or mobile device screen. Different types of touchscreens can be used under this concept: resistive, capacitive, inductive and so forth.
A disadvantage of these types of digitizers is that most of them are rigid and in many cases fragile. In addition, the fabrication of each component is hard to incorporate into a continuous roll to roll manufacturing process. This disclosure explores other alternatives that will overcome these shortcomings.